During the drilling operations of oil and gas wells, the troublesome gumbo shale formations are often encountered. Such formations, which comprise the highly reactive shale clays, lose physical and dimensional integrity when they are exposed to the pure water or the water filtration of general water-based drilling fluids. Great difficulty has always been experienced in drilling these types of shale formations.
Although the oil-based drilling fluids (pure oil drilling fluids, invert emulsion “w/o” drilling fluids and synthetic-based drilling fluids) can effectively deal with the reactive shale clay, they pose the problems of safety (due to flamability), environmental hazards (as the drilling cuttings contain hydrocarbons), and interference with oil and gas well logging operations. In order to suppress the swelling and dispersing of the shale clays in water-based drilling fluids, a variety of special water-based drilling fluids have been developed and used in field operations for many years. They are as follows:                (1) Potassium drilling fluids containing potassium salts like potassium chloride, potassium sulfate, potassium formate, potassium acetate, and partially hydrolyzed polyacrylamide (PHPA);        (2) Calcium drilling fluids containing gypsum, lime, calcium chloride or calcium nitrate;        (3) Cationic polymer drilling fluids containing quaternary ammonium organic cationic or zwitterionic polymers;        (4) MMH drilling fluids containing mixed metal hydroxides;        (5) Polyol drilling fluids containing poly-glycol or other polyol compounds;        (6) Amine drilling fluids containing organic amine or tetra-methyl ammonium;        (7) Silicate drilling fluids containing alkali metal silicates.        
The use of silicate as a drilling fluid component is well established. Silicate has been used since the 1930's as an effective means of stabilizing shale formations (U.S. Pat. No. 2,133,759). Despite being an effective shale stabilizer, silicate never achieved early, widespread success, due to certain advantages held by oil-based drilling fluids. Oil-based drilling fluids offer ease of use, are not prone to gellation or precipitation, and provide good lubricity between drill string and well bore, as measured by the coefficients of friction in the range of 0.10 to 0.18 compared with a range of 0.18 to 0.22 for water-based drilling fluids.
Recently, environmental pressures have pushed to improve the performance deficiencies in silicate drilling fluids. A suitable replacement for oil-based drilling fluids in some of the more difficult fields has been a goal of the drilling industry for many years. Many researchers have made improvements on the old silicate drilling fluids which have been used from the 1930's to 1950's. About 10 U.S. patents (U.S. Pat. Nos. 5,337,824; 5,358,044; 5,361,842; 6,152,227; 6,248,698; 6,642,183; 6,716,799; 6,806,235; 7,137,459; 7,226,895) related to silicate drilling fluids have issued since the 1990's. Recently, potassium silicate drilling fluid has become a more preferred inhibitive water-based drilling fluid for drilling reactive shale formations. The industry is witnessing increasingly successful wells drilled with potassium silicate drilling fluids. Potassium silicate drilling fluids provide very favorable well bore stability for shale sequences where traditionally only oil-based drilling fluids were successful.
Potassium silicate drilling fluids still experience high coefficients of friction between drill string and well bore, owing to the silicate coating on the surfaces, making the surfaces of drill string and well bore rough.
A few attempts have been made to improve the lubricity of silicate drilling fluids. Lubricants comprising a partial glyceride of predominantly unsaturated fatty acids having from about 16 to 24 carbon atoms (U.S. Pat. No. 6,806,235), or fatty alcohols (U.S. Pat. No. 6,716,799), or tetra alkyl ammonium (U.S. Pat. No. 6,642,183 or Canadian patent no. 2,335,762) have been disclosed for improving the lubricity of the silicate drilling fluids. The field use of these compositions has not provided favorable results.
Boundary lubricity additives typically function by adsorbing on the metal surface to form a film that will reduce metal-to-metal contact. This function is attained because the boundary lubricity additive has a polar head group that can interact with the metal surface and a tail group that is compatible with the lubricant carrier oil (mineral oil, synthetic base-stock or water). A classic example of a boundary lubricity additive is an ester which could be available as natural product (canola oil, lard oil, tall oil fatty acid etc.) or as a functionalized molecule (monobasic ester, di-ester, polyester, complex ester).
As the conditions under which metal-to-metal interactions become severe due to higher temperatures and pressures, the lubricant becomes more stressed. The distance between the metal surfaces decreases to the point where rubbing occurs and the chances for welding become greater. Traditional boundary lubrication additives do not remain on the metal surface and cannot prevent the increased friction, wear and damage to the machinery seen under these conditions. Extreme pressure (EP) additives have been used to enable specific applications operating under these conditions to continue. There are four main types of EP additives that are based on chlorinated, phosphorus, sulfur and overbased sulfonate species (see Canter N. “Special Report: Trends in extreme pressure additives” published on “TRIBOLOGY & LUBRICATION TECHNOLOGY”, September 2007, page 10˜17).
Over the past at least 20 years, there have been many discussions and some regulations enacted to limit the use of chlorinated paraffin. For example, the European Union (EU) considers the most widely used chlorinated paraffin type, known as medium chain chlorinated paraffin, to be toxic to marine life.
Canadian patent application no. 2,049,430 discloses that concentrated canola phosphatides (lecithins) are suited for use as lubricants for gear, cutting oils, finishing oils and for use in oil-based and water-based drilling fluids, due to their surprising properties of good film strength and lubricity at temperatures below 250° C.
Canadian patent nos. 1,122,594, 1,289,546, 1,340,486 and 2,273,264 disclose that sulfurized olefin and polysulfurized hydrocarbons are useful as extreme pressure additives in metal working oil.
U.S. Pat. No. 4,159,255 discloses a modified castor oil lubricant for refrigerator systems employing halocarbon refrigerants.
U.S. Pat. Nos. 5,908,814 and 6,355,600 disclose cationic polyacrylamides with lower cationic charge for use in water-based drilling fluids to suppress clay swelling.